1. Field of the Invention
The present invention relates to an air assist type fuel injection valve disposed to the intake passage of an automobile engine and for supplying fuel into a combustion chamber together with assist air.
2. Description of the Related Art
FIG. 9 is a sectional view showing a conventional fuel injection valve disclosed in, for example, Japanese Unexamined Patent Publication No. 7-103100, FIG. 10 is a partial sectional view showing the main portion of the conventional fuel injection valve shown in FIG. 9 and FIG. 11 is a top view showing an adapter used to the conventional fuel injection valve shown in FIG. 9.
As shown in the respective figures, the fuel injection valve includes an injection valve main body 1 and an adapter 2 mounted to the extreme end of the injection valve main body 1. The injection valve main body 1 includes a valve actuating system, an electromagnetic actuating system and a fuel passage system and these systems are accommodated in a housing 3 formed to a cylindrical shape.
The valve actuating system includes a stopper 4 and a valve seat main body 5 which are disposed from the upper portion to the lower portion of a valve casing section 3a formed to the lower portion of the housing 3. An accommodating section 5a is formed to the valve seat main body 5 along the center axial line thereof as well as a needle valve 6 is accommodated in the accommodating section 5a so as to move in the direction of the axial line of the needle valve 6. An injection port 5c communicating with the accommodating section 5a is formed to the extreme end surface 5b of the valve seat main body 5.
The electromagnetic actuating system includes an armature 7 which clamps the upper end of the needle valve 6, a core 9 disposed in series with the armature 7 through a spring 8, a sleeve 30 disposed internally of the core 9 and a bobbin 11 around which an electromagnetic coil is wound so as to surround the above components. The respective components 7, 8, 9, 30 which constitute the electromagnetic actuating system are accommodated in the upper portion of the housing 3. A collar section 9a is formed at a midpoint of the core 9 in the vertical direction thereof and the core 9 is fixed in the housing 3 by caulking the collar section 9a by the housing 3. A socket 13 is disposed to the housing 3 to protect a terminal 12 connected to the electromagnetic coil 10 and to fit and connect to another terminal.
The fuel passage system includes a filter 14 mounted on the upper end of the core 9, a first fuel passage 15a formed in the sleeve 30 so that the fuel supplied through the filter 14 passes therethrough, a second fuel passage 15b formed in the armature 7 along the axial line thereof continuously from the first fuel passage 15a and a third fuel passage 15c formed between the accommodating section 5a of the valve seat main body 5 and the outer periphery of the needle valve 6 continuously from the second fuel passage 15b.
The adapter 2 includes two air/fuel mixing passages 19 having a circular cross section into which the fuel injected from the injection port 5c of the injection valve main body 1 is introduced and air passages 20 opened to the respective air/fuel mixing passages 19 for supplying air thereinto. The adapter 2 causes the fuel injected into the air/fuel mixing passages 19 to collide against the air from the air passages 20 to thereby make the fuel to fine particles. The two air/fuel mixing passages 19 are formed symmetrically with respect to the center axial line of the injection port 5c with the centerlines thereof intersecting at a point on the center axial line of the injection port 5c. Further, the edge portions of the openings formed to the upstream end surfaces of the respective air/fuel mixing passages 19 are in contact with each other on the center axial line of the injection port 5c.
The fuel injection valve is mounted on a holder 21 which is formed integrally with an intake passage communicating with the combustion chamber of a cylinder. An air introducing nipple 22 is mounted on the holder 21.
An air supply passage 23 is formed between the outer peripheral surface of the adapter 2 and the inner peripheral surface of the holder 21. Air is introduced from the air introducing nipple 22 into the air supply passage 23 and supplied to the respective air/fuel mixing passages 19 through the air supply passage 23 and the respective air passages 20.
A plate 24 is interposed between the extreme end surface 5b of the valve seat main body 5 and the adapter 2 in intimate contact with both of them. The plate 24 is fixed in the state that it is in intimate contact with the extreme end surface 5b of the valve seat main body 5 and respective parts are made so that the plate 24 comes into intimate contact with the adapter 2 when the adapter 2 is mounted on the injection valve main body 1. Circular orifice holes 24a are formed to the plate 24 each opposing each air/fuel mixing passage 19. Therefore, the orifice hole 24a is connected directly to the air/fuel mixing passage 19 without interposing a fuel flow divider therebetween. Since the opening 28 of the air passage 20 is formed on each of the air/fuel mixing passages 19 at a position a prescribed distance apart from the end surface of the plate 24 toward a downstream side, the portion of the air/fuel mixing passage 19 located downstream of the opening 28 serves as the air/fuel mixing passage substantially.
As apparent from FIG. 9 and FIG. 10, the total area of the openings of the two orifice holes 24a is set smaller than the opening area of a seat section 5d when the needle valve 6 moves in the upward direction to thereby open the valve. As a result, in the fuel injection, a uniform pressure chamber 5e where the pressure of fuel is made uniform is formed in a space on the fuel upstream side of the plate 24. The fuel injection quantity supplied to each respective air/fuel mixing passage 19 is determined by the area of each orifice hole 24a which corresponds to each air/fuel mixing passage 19. Accordingly, the same amount of fuel is uniformly supplied to each air/fuel mixing passage 19 from each orifice hole 24a having the same diameter. Further, each of the orifice holes 24a is formed directing to each of the openings 28 of the air passages 20.
An O-ring 25 is interposed between the lower end of the adapter 2 and the lower end surface of the holder 21 so that they are held in an air tight state.
Next, the operation of the conventional fuel injection valve will be described.
When fuel is supplied to the fuel injecting system, it is filtered with the filter 14 and reaches the seat section 5d of the valve seat main body 5 through the first, second and third fuel passages 15a, 15b and 15c.
When the electromagnetic actuating system of the fuel injection valve is actuated, the needle valve 6 is driven and moved upward, the seat section 5d of the valve seat main body 5 is opened and the fuel is injected from the injection port 5c. Since the uniform pressure chamber 5e is filled with the fuel and a uniform pressure is applied to the plate 24 confronting the injection port 5c at the time, the fuel is injected into the respective air/fuel mixing passages 19 while being uniformly distributed by the circular orifice holes 24a having the same diameter. That is, the flow rates of the fuel to be injected into the respective air/fuel mixing passages 19 are determined by the open areas of the orifice holes 24a and, as a result, the fuel is separately supplied into the respective air/fuel mixing passages 19 while being accurately measured by the respective orifice holes 24a.
Since the fuel is separately supplied by the orifice holes 24a of the plate 24, it can be uniformly injected. Moreover, since the fuel is held once in the uniform pressure chamber 5e and then injected into the air/fuel mixing passages 19, the collision of the injected fuel against the air/fuel mixing passages 19 is restricted and thus it is also restricted that the injected fuel drops into an engine cylinder in the form of droplets. On the other hand, assist air is introduced from the air introducing nipple 22 into the air supply passage 23 and supplied into the respective air/fuel mixing passages 19 from a lateral direction through the respective air passages 20. The thus supplied assist air is collided against the fuel supplied from the orifice holes 24a to thereby make the fuel to fine particles. The fuel is injected into each combustion chamber in an amount distributed by the orifice holes 24a.
In the conventional fuel injection valve arranged as described above, a fuel branch section need not be formed to the adapter 2 because fuel is uniformly divided by the orifice holes 24a of the plate 24 and passes through the air/fuel mixing passages 19. Therefore, the adapter 2 can be molded from resin which can be very easily processed as compared with a case that the adapter 2 is composed of metal because it is not required to correctly machine the adapter 2 to flow fuel in an uniformly divided amount.
In the conventional fuel injection valve, however, since the edge portions of the openings formed to the upstream end surfaces of the two air/fuel mixing passages 19 are formed to come into contact with each other on the center axial line of the injection port 5c, the partition wall between the two air/fuel mixing passages 19 forms an edge to the upstream end surfaces. As a result, there is a problem that when the adapter 2 is molded from resin, the edge section is chipped off because the resin does not flow well so that the edge is formed to a little short shape and the distribution of fuel is adversely affected thereby.
To improve the problem of the conventional fuel injection valve, there is contemplated a method that the partition wall between the two air/fuel mixing passages 19 does not form an edge to the upstream end surfaces by shifting the positions where the two air/fuel mixing passages 19 are formed toward the outside of the fuel injection valve in a radius direction. In this case, however, the directions in which fuel is injected from the orifice holes 24a are greatly displaced from the passage centers of the two air/fuel mixing passages 19 by the shift of the positions where the air/fuel mixing passages 19 are formed toward the outside in the radial direction. Accordingly, there is caused a problem that a mixed gas cannot be formed well.
To cope with the above problem, it is also contemplated to shift the positions where the orifice holes 24a are formed toward the outside in the radial direction in accordance with the positions where the air/fuel mixing passages 19 are formed or to increase the inclination of the hole axis (fuel injecting angle) of the orifice holes 24a. In these cases, however, there arises a problem that it is difficult to punch many holes to the plate 24 by a press machine and productivity is lowered thereby. Further, the shift of the positions where the orifice holes 24a are formed toward the outside in the radius direction increases the volume of a dead space formed upstream of the plate 24. When fuel is not injected, there exists fuel to which no fuel pressure is applied in the dead space and further the amount of the fuel changes by the evaporation of it. Thus, there is a problem that since the amount of fuel in the dead space is greatly dispersed by an increase of the dead space, an amount of fuel to be injected cannot be correctly controlled when the injection of fuel is resumed.
As described above, it is required to a fuel injection valve that the dislocation between the directions in which fuel is injected from the orifice holes 24a and the passage centers of the air/fuel mixing passages 19 is suppressed as well as the volume of a dead space is reduced. Further, it is necessary to dispose the openings formed to the upstream end surfaces of the air/fuel mixing passages 19 in close proximity to each other.